Technological advances have permitted semiconductor integrated circuit memory devices to comprise significantly more circuit elements in a given silicon area. Reducing and eliminating defects in the circuit elements has, however, become increasingly more difficult with the increased number of circuit elements. To achieve higher population capacities, circuit designers strive to reduce the size of individual circuit elements to maximize available die real estate. The reduced size makes these circuit elements increasingly susceptible to defects caused by material impurities during fabrication.
Relying on zero defects in the fabrication of integrated circuit memory devices is an unrealistic goal, however. Therefore, redundant circuit elements are provided on the devices to reduce the number of scrapped devices. If a primary circuit element of a device is determined to be defective, a redundant circuit element is substituted for the defective primary circuit element. Substantial reductions in scrap are achieved by using redundant circuit elements without substantially increasing the cost of the device.
However, occasionally a defective circuit element of a device cannot be repaired by using a redundant element also within the device, or such repair is economically or logistically unfeasible. For example, a single bit failure may be serious enough that it is not internally repairable. In this and other situations, the entire memory device may be replaced by a redundant device. There are drawbacks to this approach, however. Even if the memory device is only partially defective, replacing it with a redundant device means that many of the operational elements are not used and thus wasted. Furthermore, the redundant device must itself be completely operational, or otherwise the replacement will not be successful.
Complete replacement of a defective memory device with a redundant device may therefore be economically undesirable in that a nearly operational device must be scrapped and replaced by a completely operational device. For these reasons, and for other reasons stated below which will become apparent to those skilled in the art upon reading and understanding the specification as disclosed herein, there is a need for the replacement of a partially defective integrated circuit device without having to completely replace the partially defective device. That is, there is a need to partially replace the defective device such that use is still made of many, most or all of the operational elements of the partially defective device.